This one is something special. I’d call it a flat pattern, too. Very well done, sir!
Source GetDiscount
Remixed from a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
Sweet and subtle white plaster with hints of noise and grunge.
Source Phil Maurer
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Based on several public domain drawings on Wikimedia Commons. This was formed from a rectangular tile. The tile can be accessed in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
Zero CC tileable hard cover cells book texture, 4k, scanned and made by me. CC0
Source Sojan Janso
From a drawing in 'Cassell's Library of English Literature', Henry Morley, 1883.
Source Firkin
Could be paper, could be a Polaroid frame – up to you!
Source Chaos
You know, tiny and sharp. I’m sure you’ll find a use for it.
Source Atle Mo
White circles connecting on a light gray background.
Source Mark Collins
From a drawing in 'Friend or Fortune? The story of a strange year', Robert Overton, 1897.
Source Firkin
Might not be super subtle, but quite original in its form.
Source Alex Smith
Prismatic Geometric Pattern Background
Source GDJ
Zero CC tileable seed texture, edited by me to be seamless from a Pixabay image. CC0
Source Sojan Janso
Prismatic Groovy Concentric Background 4 No Black
Source GDJ
To get the tile this is formed from select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
A free seamless background with pink spots.
Source V. Hartikainen
The texture of this background image has some similarities with leather, and it's colored in a dark brown color. So, if you are looking for a dark brown background image for your website, this may be an option for you.
Source V. Hartikainen
Adapted heavily from a JPG that was uploaded to Pixabay by Viscious-Speed.
Source Firkin
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
The edges of all the red objects line up either vertically or horizontally, but it doesn't appear so. Made from a square tile that can be got by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Background formed from the original with an emboss effect
Source GDJ